The objectives of the proposed research are to determine the most important mutagenic chemical compounds present in atmospheric particulate matter and in urban source effluents using newly developed human cell assays. The results on concentrations of the most important mutagens in the ambient organic aerosols and source samples will be used to track those compounds back to their source. The research initially will involve ambient organic particulate matter samples representative of the full range of seasonal conditions and spatial pollutant gradients found in the heavily polluted Los Angeles area atmosphere. Bioassay-directed chemical analysis will be used to determine the identity of the most important mutagens. An integral part of the study will be the determination of the effect of atmospheric transformations on the composition and concentrations of the most important mutagens. One measure of atmospheric transformation is the difference between the observed atmospheric concentrations of the most important mutagens and the values calculated from the contributions of the primary sources. The calculated values will be obtained using either atmospheric transport models that follow dispersion from the sources or molecular tracer techniques. Another measure is provided by the distribution of the primary mutagens between the different size fractions of the fine aerosols in the atmosphere. Particles in the 0.05 to 0.5 mum size range are representative of primary effluents whereas particles in the size range of 0.5 to 2.0 mum have undergone atmospheric reactions and agglomeration in the atmosphere. An understanding of the partitioning of PAH and its atmospheric transformation products is important for the interpretation of the data on the distribution of the most important mutagen between the different size fractions. Preliminary results with human cell assays on fractions, obtained by gradient elution liquid chromatography, of extracts from particles collected in Los Angeles, CA, Saint Louis, MO, and Washington, DC, show that polycyclic aromatic hydrocarbons (PAH) and their nitro derivatives are two classes of compounds that account for a significant portion of the observed mutations. While the PAH are emitted primarily by combustion sources, the nitro-substituted PAH may be either present in the primary effluents from the combustors or be produced from combustion- generated PAH by atmospheric reactions. The mechanism of formation of PAH and its derivatives will be studied in order to help distinguish between the combustion and atmospheric pathways to nitro-substituted PAH as well as to explain the observation of high specific mutagenicity (mutant fraction per microgram of organic carbon) of certain combustion sources (e.g., natural gas appliances). Key to the mechanism is the measurement of the PAH radicals in flames. The transferability of the results from Los Angeles to other locations, after due allowance is made for differences in the magnitudes of the major sources of organic emission and for differences in dispersion and atmospheric chemistry, will be assessed by studying samples from two locations in each of Rochester, NY, and Woburn, MA, and selected indoor samples.